Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$34.47	12.609%	$38.8163	$38.82	$38.80	$38.80
Purchase #2	$55.30	7.306%	$59.3402	$59.34	$59.35	$59.30
Purchase #3	$135.81	4.803%	$142.333	$142.33	$142.35	$142.30
Purchase #4	$151.44	7.217%	$162.3694	$162.37	$162.35	$162.40
Purchase #5	$108.38	8.520%	$117.614	$117.61	$117.60	$117.60
Purchase #6	$12.79	11.810%	$14.3005	$14.30	$14.30	$14.30
Purchase #7	$131.78	5.107%	$138.51	$138.51	$138.50	$138.50
7 purchase totals =	$629.97		$673.2834	$673.28	$673.25	$673.20